Run unused functions reported by cppcheck
This change removes a few (but not all) unused functions.
Some unused helper functions were not removed due to their complexity and potential of future use.
ServerEnvironment is a huge class with many accessors. In various places it's not needed
Remove it to reduce the ServerEnvironment view.
Idea here is to reduce size of some of our objects to transport lightweight managers and permit easier testing
Pathfinder is now tied to a generic map, not a ServerMap, it can be
ported to client
* Rename IWritableNodeDefManager to NodeDefManager
* Make INodeDefManager functions const
* Use "const *NodeDefManager" instead of "*INodeDefManager"
* Remove unused INodeDefManager class
* Merge NodeDefManager and CNodeDefManager
* Document NodeDefManager
